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Organic Reactions and their
Mechanisms Third Edition
P S KALSI Formerly
Dean of Colleges, Punjab Technical University Jalandhar, India
and Professor & Head, Department of Chemistry College of Basic Sciences and Humanities
Punjab Agricultural University, Ludhiana, India
New Age Science Limited The Control Centre, 11 A Little Mount Sion
Tunbridge Wells, Kent TNI 1YS, UK www.newagescience.co.uk • e-mail: [email protected]
Contents
Chapter 1 Fundamental Principles and Special Topics
1.1 Structure and Bonding in Organic Compounds
1.2 Electronegativity—Dipole Moment
1.3 Inductive and Field Effects
1.4 Hydrogen Bond
1.5 Other Weaker Bonds
1.6 Bond Dissociation Energy
1.7 The Hammett Equation—Linear Free Energy Relationship
1.8 Taft Equation
1.9 Steric Effects, Strain and Bredt Rule
Problems
Answers to the Problems
Chapter 2 Delocalized Chemical Bonding
2.1 1, 3-butadiene a Typical Conjugated System
2.2 Resonance
2.3 Aromaticity
2.4 The Terms Aromatic, Antiaromatic and Nonaromatic
2.5 Annulenes
2.6 The Frost Circle—Molecular Orbital Description of Aromaticity and Antiaromaticity
2.7 Aromatic and Antiaromatic Ions
2.8 Other Non-Benzenoid Aromatic Compounds
2.9 Heterocyclic Aromatic Compounds
2.10 Metallocenes and Related Compounds
2.11 Fused Benzenoids and Fullerenes
2.12 Homoaromatic Compounds
2.13 Hyperconj ugation
2.14 Hexahelicene
xv
xvi CONTENTS
2.15 Tautomerism 79
Problems 83
Answers to the Problems 85
Chapter 3 Organic Acids and Bases 87-121
3.1 The Bronsted-Lowry Concepts of Acids and Bases 87
3.2 The Lewis Definition of Acids and Bases 90
3.3 The Relation Between Structure and Acidity 91
3.4 Bases 106
3.5 Relation Between Structure and Basicity 106
3.6 Synthetic Applications of Lithium Diisopropylamide (LDA) 114
3.7 Acid-Base Reactions 116
3.8 The Effects of the Solvent on Acid and Base Strength 117
3.9 Leveling Effect 118
3.10 Hard and Soft Acids and Bases 118
Problems 119
Answers to the Problems 119
Chapter 4 Organic Reactions and the Determination of 122-175 their Mechanisms
4.1 Mechanistic Classification 122
4.2 Nucleophiles and Electrophiles 130
4.3 Electron Movement 131
4.4 Equilibria and Free Energy 131
4.5 Free Energy Change in Relation to Bond Strengths and
Degree of Order in a System 132
4.6 Reaction Rates 134
4.7 The Transition State—Activation Energy 135
4.8 Transition State Theory—Measurement of Activation Energy 135
4.9 Reaction Profile Diagrams 137
4.10 The Rate Determining Step 138
4.11 Thermodynamic and Kinetic Control 139
4.12 Applications of Kinetic Principles 141
4.13 The Curtin-Hammett Principle—Importance of Transition State 144
4.14 Microscopic Reversibility 145
4.15 Methods of Determining Mechanisms 146
4.16 Reactive Intermediates 154
Problems 174
Answers to the Problems 175
CONTENTS xvii
Chapter 5 Aliphatic Nucleophilic Substitution and 176-215 its Synthetic Applications
5.1 Introduction 176
5.2 Synchronous Substitution—SN2 Process 182
5.3 Substitution by Ionization—SN1 Mechanism 196
5.4 SN1 Versus SN2 Reactions 198
5.5 Other Aliphatic Substitution Pathways 200
5.6 The Role of Ion Pairs 202
5.7 Neighbouring Group Participation and Nonclassical Carbocations 204
5.8 Nucleophilic Substitution at Silicon 212
Problems 212
Answers to the Problems 214
Chapter 6 Common Organic Reactions and their 216-262 Mechanisms
6.1 Base Catalysed Reactions (Formation of Carbon-Carbon Bonds) 216
6.2 Stork Enamine Reactions (Formation of Carbon-Carbon Bonds)— 239 Reaction of an Enamine with Reactive Electrophiles
6.3 Acid Catalysed Reactions (Formation of Carbon-Carbon Bonds) 246
6.4 Reactions of Carboxylic Acids and their Derivatives 250
6.5 Hydrolysis of Amides 257
Problems 258
Answers to the Problems 260
Chapter 7 Reagents in Organic Synthesis and Relevant 263-328 Name Reactions
7.1 Organotransition Metal Reagents 263
7.2 Some Transition Metal Organometallic Reactions 266
7.3 Phosphorus Containing Reagents 280
7.4 Organosulphur Compounds: Sulphur Ylides 289
7.5 Silicon Reagents 297
7.6 Boron Containing Reagents 304
7.7 Organometallic Reagents 316
Problems 326
Answers to the Problems 327
XVIII CONTENTS
Chapter 8 Electrophilic Aromatic Substitution 329-365
8.1 General View—The Arenium Ion—The Arenium Ion Mechanism—S„2 Reaction 329
8.2 Electrophilic Substitution on Monosubstituted Benzenes—Orientation 340 and Reactivity
8.3 Electrophilic Substitution in Naphthalene and Larger Polycyclic 352 Aromatic Hydrocarbons
8.4 Attack of the Electrophile at a Carbon already Bearing a Substituent 353 (Ipso Position)—Ipso Substitution
8.5 Aromatic Rearrangements 355 8.6 Some Name Reactions 357
8.7 Electrophilic Substitution on Heteroaromatic Compounds 358
8.8 Diazonium Coupling 361
Problems 362
Answers to the Problems 363
Chapter 9 Aromatic Nucleophilic Substitution 366-379
9.1 The SNAr Mechanism—The Addition—Elimination Mechanism— 366 The General Nucleophilic Aromatic Ipso Substitution
9.2 The SN1 Mechanism in Nucleophilic Aromatic Substitution— 369 The Aryl Cation Mechanism—Diazonium Salts
9.3 Nucleophilic Aromatic Substitution by Elimination—Addition— 370 The Benzyne Mechanism
9.4 Benzyne—A Strained Cycloalkyne 373
9.5 Nucleophilic Substitution of Pyridine—The Chichibabin Reaction 376
9.6 Nucleophilic Substitution to Arenechromium Carbonyl Complexes 376
Problems 378
Answers to the Problems 378
Chapter 10 Photochemistry 380-420
10.1 Absorption of Electromagnetic Radiation—Quantum Yield 380
10.2 Excited States 381
10.3 The Fate of the Molecule in Sx and Tx States (Jablonski Diagram) 381
10.4 Energy Transfer 383
10.5 Energy Transfer and Photosensitization 383
10.6 Forbidden Transitions—Intersystem Crossing 384
10.7 Photochemical Reactions 385
Problems 415
Answers to the Problems All
CONTENTS xix
Chapter 11 Addition to Carbon-Carbon and Carbon-Hetero 421-437 Multiple Bonds
11.1 Addition of Electrophiles to a Multiple Bond 421
11.2 Nucleophilic Additions to Alkenes and Alkynes 432
11.3 Addition of Carbenes 433
11.4 Nucleophilic Additions to Carbonyl Compounds 434 (Aldehydes and Ketones)
11.5 Nucleophilic Additions to the Carbonyl Carbon of a Carboxylic 435 Acid Derivative
11.6 Radical Additions to Alkenes 436
11.7 Nucleophilic Attack on Carbon-Nitrogen Triple Bond 436
Problems 437
Answers to the Problems 437
Chapter 12 Elimination Reactions 438-461
12.1 The Bimolecular Mechanism for Elimination—E2 Process 439
12.2 The Unimolecular Mechanism for Elimination—El Process 451
12.3 Pyrolytic syn Elimination—Ei—Elimination Internal 454
Problems 458
Answers to the Problems 459
Chapter 13 Oxidation Methods 462-499
13.1 Oxidation of Alcohols to Aldehydes, Ketones or Carboxylic Acids 462
13.2 Allylic Oxidation of Alkenes 469
13.3 Oxidation of Saturated C—H Groups 470
13.4 Addition of Oxygen at Carbon-Carbon Double Bonds 474
13.5 Ozonolysis 485
13.6 Cleavage of Glycols and Related Compounds 486
13.7 Oxidation of Alkenes to Aldehydes and Ketones Catalysed with 488 Palladium and Oxidation of Alkylboranes
13.8 Oxidation of Ketones 490
13.9 Oxidation of a-Ketols 493
13.10 Oxidative Decarboxylation of Acids 493
13.11 Aromatic Rings of Phenols—Coupling 494
13.12 Oxidation of Amines 495
13.13 Photooxidation of Alkenes 495
Problems 496
Answers to the Problems 498
XX CONTENTS
Chapter 14 Reduction Methods 500-542
14.1 Catalytic Reduction-Reduction with Diimide and Hydroboration 501 14.2 Reduction by Dissolving Metals—Metal and Ammonia 510 14.3 Addition of Hydrogen and Reductive Coupling of Carbonyl 515
Compounds—Dissolving Metal Reductions 14.4 Reductive Removal of Functional Groups and Reductive 516
Fission—Hydrogenolysis 14.5 Reductive Deoxygenation of Carbonyl Groups 519 14.6 Reduction by Hydride Transfer Reagents 522 14.7 Stereoselectivity of Reduction with Small Hydride Donors 529
14.8 Stereoselectivity of Reduction with Hindered Hydride 531 Donors-Selectride
14.9 Chiral Boranes—Enantioselective Reduction of Carbonyl 533 Compounds
14.10 Meerwein-Ponndorf Reduction—The Hydride Transfer 534 Reaction
14.11 Cannizzaro Reaction 535 14.12 Reduction of Aldehydes and Ketones with an Adjacent 535
Stereocenter (Asymmetric Induction) 14.13 Reduction of Epoxides 537 14.14 Reductions with Enzymes—Bakers Yeast 538
14.15 Less Reactive Modified Borohydrides—Sodium Cyanoborohydride 539 and Sodium Triacetoxyborohydride Problems 541
Answers to the Problems 541
Chapter 15 Molecular Rearrangements 543-568
15.1 Rearrangements to Electron Deficient Carbon 545
15.2 Rearrangements to Electron Deficient Nitrogen 554
15.3 Rearrangements to Electron Deficient Oxygen 559
15.4 Rearrangement to Electron Rich Carbon 560
15.5 Aromatic Rearrangements 565
15.6 Free Radical Rearrangements 566
Problems 566
Answers to the Problems 567
Chapter 16 Free Radical Reactions 569-604
16.1 Structure, Stability and Geometry 569
16.2 Preparation 569
16.3 Properties of Free Radicals 574
CONTENTS xxi
16.4 Aromatic Nucleophilic Subst i tut ion—S^l Substitution 588
16.5 Homolytic Aromatic Substitution 589
16.6 Some Name Reactions 590
16.7 The Coupling of Alkynes 595
16.8 Reactions Involving Electron Transfer Steps 596
16.9 Molecular Rearrangements 597
16.10 Some Further Substitution and Other Reactions 599
Problems 602
Answers to the Problems 603
Chapter 17 Pericyclic Reactions 605-682
17.1 Conservation of Molecular Orbital Symmetry 608
17.2 Methods to Explain Pericyclic Reactions 608
17.3 Electrocyclic Reactions (FMO-Approach) 609
17.4 Cycloadditions (FMO-Approach) 630
17.5 1, 3-Dipolar Cycloadditions 644
17.6 Cheletropic Reactions 645
17.7 Sigmatropic Rearrangements 647
17.8 The ENE Reaction 663
17.9 Aromatic Transition States 664
17.10 Möbius-Hückel Analysis (PMO) Approach 665
17.11 Correlation Diagram Method 671
Problems 676
Answers to the Problems 679
References and Fur ther Reading 683-684
Index 685-693
